This invention relates to pyrotechnic lamps and more particularly, to lasers utilizing the radiation generated from certain exothermic, pyrotechnic reactions to directly pump the laser rod.
In U.S. Pat. No. 4,371,969 entitled "LOW-COST LASER", by Evan Chicklis and James Mosto, also assigned to the common assignee of this application, there is described a low-cost, compact laser in which a solid state laser rod is pumped by a pump source consisting of the burning of a pure metal in a flowing oxygen atmosphere. In one embodiment, the pump source comprises a zirconium metal foul wound about a graphite rod and enclosed in a tube to which flowing oxygen is admitted. Ignition of the metal foil is achieved by applying a large current to the graphite rod. The pump described therein is relatively compact, has minimum smoke and soot associated therewith, and permits laser operation in excess of one second.
Such a laser is shown in FIG. 1, which generally corresponds to the single figure of the above-mentioned Chicklis/Mosto patent. As shown therein, the low-cost laser includes a laser rod assembly 10, including a laser rod 11 of one of several materials well known to those skilled in the art. The ends of the laser rod 11 are coated to provide the reflective and partially reflective mirrors for the laser cavity in the usual manner. Optionally, of course, separate mirrors could be provided. The laser rod 11 is disposed within a transparent tube 12, typically of quartz. End caps 14 and 16 are provided at the end of case 12 and have holes therein to accommodate stems 18 and 20. The functions of the stems 18 and 20 is to allow a coolant to be supplied to the tube 12 to cool the laser rod 11, if required.
Positioned next to the laser rod assembly 10 is the pump source 22 therefor. In the apparatus of the Chicklis/Mosto patent, the pump is a pyrotechnic lamp comprising a composite rod 24 disposed within a transparent tube 26, also made of quartz. As shown in greater detail in the cross-section of FIG. 2, the rod 24 comprises a graphite rod 25 having zirconium metal foil 27 wrapped thereabout. The ends of the tubes 26 have end caps 28 and 30 thereon for accommodating stems 32 and 34 to allow flowing oxygen to be applied to the tube 26. The graphite rod 25 is secured within graphite terminals 35 positioned within the end caps 28 and 30 and preferably held therein with a set screw, not shown.
The metal foil 27 is described as being preferably spiral wrapped about a rod and then slipped over the graphite rod 25 before the graphite terminals 35 are attached by press-fitting to each end of the graphite rod. As thus constructed, the spiral wrapped foil cylinder 27 is free to move on the graphite rod 25 but is limited by the graphite terminals 35 at each end.
The laser rod assembly 10 and the pump source 22 are disposed within a housing comprising an upper housing portion 36 and a lower housing portion 38. These portions are of metal and are fastened together by screws 40. The interior portions 42 and 44 of the upper 38 and lower 36 housing portions are reflective, which collect and image radiation from the pump source 22 onto the laser rod 11. The housing also includes two end sections 46 (only one of which is shown in the figure). The end sections are fastened to the lower and upper housing portions 36, 38 by means of screws 48. The end sections have holes 50, 52 therein for accommodating the stems 18, 20, 32 and 34.
For an expendable laser, the flowing oxygen can be supplied by a cartridge or chemical oxygen source (such as KClO.sub.4) attached to stem 34. Inert gases may also be added to the flowing gas stream as the applicants have found that they increase produced obscurant removal. When the metal foil is ignited by applying an electrical current to the graphite rod (or by using a separate squib) it is burned in the oxygen environment outputting a sufficient amount of optical radiation to pump the laser rod 10, such that laser radiation is emitted from hole 52 in the end section.
The pyrotechnic lamp as employed in the above-described, low-cost laser can also be used for other purposes. In many applications, however, it has certain drawbacks which would make it more desirable if corrected. For one, the optical radiation output of the wrapped foil is not reproduceable. Moreover, a longer and more reproduceable burn duration as well as more uniform heating and ignition, coupled with less energy required for ignition, would be desirable. Additionally, it has been found that in some instances, part of the zirconium melts down to the quartz tube 26 and destroys the envelope.
Wherefore, it is the object of the present invention to provide an improved pyrotechnic lamp for use within an environment such as the low-cost laser of Chicklis/Mosto or in other separate applications which eliminates the above-described shortcomings of a pyrotechnic lamp employing zirconium metal foil wrapped about a graphite rod within a quartz tube, and the like, such as zirconium powder/pellet pumped lasers.